BioMarin Pharmaceutical Inc. re-acquired the Canadian rights for tetrahydrobiopterin (BH4), including Kuvan (sapropterin dihydrochloride), from Merck Serono, a division of Merck KGaA.

The terms of the agreement specify a reduction in royalties owed to BioMarin on Merck Serono sales outside the United States and Japan. Based on the structure of the amended agreement, the reduction in royalties cannot exceed an undisclosed cap.

Kuvan is an oral small molecule for the treatment of phenylketonuria (PKU) developed in partnership with Merck Serono. Based on published literature, there are approximately 1,200 to 1,500 people under the age of 40 with PKU in Canada.

"Acquiring rights to Kuvan in Canada allows BioMarin to better coordinate commercialisation efforts in the North American market," said Stephen Aselage, senior vice president, Global Commercial Development, BioMarin. "This agreement with Merck Serono comes at an exciting time for the company and the PKU community after Kuvan was approved in the United States last week."

Kuvan (sapropterin dihydrochloride) Tablet is indicated to reduce blood phenylalanine (Phe) levels in patients with hyperphenylalaninemia (HPA) due to tetrahydrobiopterin- (BH4-) responsive phenylketonuria (PKU). Kuvan is to be used in conjunction with a Phe-restricted diet.

The active ingredient in Kuvan, sapropterin dihydrochloride, is the synthetic form of 6R-BH4 (tetrahydrobiopterin), a naturally occurring enzyme cofactor that works in conjunction with phenylalanine hydroxylase (PAH) to metabolize Phe. BioMarin and Merck Serono estimate that Kuvan could be a potential treatment option for approximately 30 percent to 50 percent of the estimated 50,000 identified PKU patients in the developed world.

Kuvan has received orphan drug designation from both the US FDA and the European Medicines Agency (EMEA). Kuvan has received seven years of market exclusivity in the US. In November 2007, Merck Serono submitted a marketing authorization application (MAA) to the EMEA for sapropterin dihydrochloride as an oral treatment for patients suffering from HPA due to PKU or BH4 deficiency. If approved in the EU, it will receive 10 years of market exclusivity for this indication.

PKU, a genetic disorder affecting approximately 50,000 diagnosed patients in the developed world, is caused by a deficiency of the enzyme phenylalanine hydroxylase. PAH is required for the metabolism of phenylalanine, an essential amino acid found in most protein-containing foods. If the active enzyme is not present in sufficient quantities, Phe accumulates to abnormally high levels in the blood and becomes toxic to the brain, resulting in a variety of complications including severe mental retardation and brain damage, mental illness, seizures, tremors, and limited cognitive ability.